int idate ( string $format [, int $timestamp ] ) - Returns a number formatted according to the given format string using the given integer timestamp or the current local time if no timestamp is given.

array localtime ([ int $timestamp [, bool $is_associative ]] ) - The localtime() function returns an array identical to that of the structure returned by the C function call.

mixed microtime ([ bool $get_as_float ] ) - microtime() returns the current Unix timestamp with microseconds. This function is only available on operating systems that support the gettimeofday() system call.

int strtotime ( string $time [, int $now ] ) - This function will use the TZ environment variable (if available) to calculate the timestamp. Since PHP 5.1.0 there are easier ways to define the timezone that is used across all date/time functions.

int time ( void ) - Returns the current time measured in the number of seconds since the Unix Epoch (January 1 1970 00:00:00 GMT).